There is no way to look up Bundle Identifiers in the App Store at this time. To find a bundle identifier, you will need to look at a file inside the app.
Finding an app's bundle identifier in an iTunes Library - If you sync your device with iTunes and the app you desire is either on your device, or was downloaded through iTunes, it will exist on your computer's hard drive. You can locate it on your hard drive and look inside the app to find the bundle identifier.